| 摘要 |
PROBLEM TO BE SOLVED: To realize protection of an inverter easily and surely at the time of a DC mode by determining the output detection current value and the difference between the output detection current value and a reference current value during the DC mode brake interval thereby controlling the output voltage of an inverter such that the detection current value is limited within the reference current value. SOLUTION: During the DC exciting interval before starting an AC motor 3 or during the brake interval after stop control, an inverter 2 is controlled to produce a DC output voltage by a conversion switch. Effective value or mean value of the output current is then determined, as a detection current value, by a current detector 5a-5c coupled with a three-phase output line 4a-4c. Subsequently, the difference between the detection current value and a reference current value of a DC reference generating means in an overcurrent protector 8 is determined and a conversion switch Q1-Q6 for the inverter 2 is controlled to limit the detection current value within the reference current value based on a value corresponding to the difference thus facilitating overcurrent protection under DC mode. |
